The present invention relates to a joint prosthesis and method of producing same.
Within this application several publications are referenced by arabic numerals within parenthesis. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of all of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
Various joint prostheses have been designed and produced, such as the Swanson trapezial implant, the Swanson condylar implant, the De la Caffiniere prosthesis, the Braun design, the Kessler design, the Mayo clinic prosthesis, the Helal spacer, the Eaton trapezial implant, and the Niebauer "tie-in" design.
In addition, various patents have been granted on joint prostheses and methods of making them. For example, U.S. Pat. No. 4,704,686 to Aldinger ("Aldinger") relates to the fabrication of bone replacement prosthesis using tomography. Specifically, tomographic pictures of cross-sections of the bone are taken to determine characteristics of the bone, such as the locations of different bone densities. This data is then used to calculate the size and placement of a series of disks which when connected form the desired prosthesis shape. The prosthesis is machined according to these calculations. The use of bone cement is minimized or eliminated because the accurate shape of the resulting prosthesis leaves little space between the prosthesis and the remaining bone.
Although Aldinger discusses the custom fabrication of prostheses based on the shape and density of the patient's bone so that a prosthesis can be press-fit into the bone, the patent does not teach the use of imaging data to custom fabricate anatomic articular surfaces for the joint itself. In this regard it is noted that as used herein the terms "anatomic" and "anatomically accurate" may relate to shapes that are either calculated or stored in a database. Moreover, it is noted that the term "spline surfaces" is a general term that includes both biquintic and B-spline surfaces, for example.
In U.S. Pat. No. 5,037,440 to Koenig ("Koenig"), each anchor stem of a prosthesis is press-fit into a hole created in the bone on a respective side of the joint. One anchor has a complex convex surface which wraps around the end of the bone and the other anchor has a complex concave surface. The only contact between the anchors, which are not attached, are the complex surfaces which can slide against each other. The surfaces are not, however, anatomically correct.
U.S. Pat. No. 4,725,280 to Laure ("Laure'280") shows a saddle-like finger joint prosthesis having a "V"-shaped tab anchor and a valley-shaped slot anchor. Specifically, the "V"-shaped tab anchor has concave sides and the slot anchor has convex sides. Since the tab anchor slides along the bottom of the valley of the slot anchor, undesired sideward movement of the joint is restricted. While the two anchors are not attached to each other, the prosthesis does not provide for two anatomically correct contact and load-bearing surfaces.
U.S. Pat. No. 4,276,660 to Laure ("Laure'660") relates to a thumb joint prosthesis that utilizes a ball and socket configuration. Again, this patent does not teach anatomically correct contact and load-bearing surfaces.
U.S. Pat. No. 5,150,304 to Berchem et al. ("Berchem et al.") relates to a method of fabricating an implantable joint prosthesis. Specifically, a computer determines the shape of the joint prosthesis before surgery from computations, such as finite element analysis, so that undercuts can be eliminated and so that the stress is uniformly distributed. The computations are based on data received from imaging scans of the patient's bone. Once the shape of the bone is determined the prosthesis is either selected from a collection of prostheses or machined using computer-aided manufacturing.
While the Berchem et al. patent discusses the use of a mathematical model for making a joint implant prosthesis based on imaging results of the patient's bone, there is no teaching to use mathematically described anatomic joint surfaces derived from the examination of other joints to create the prosthesis. Furthermore, unlike the anatomically correct joint surfaces of the subject invention, the non-articular surface is tailored to reduce stress and not to recreate a healthy articular joint surface.
U.S. Pat. No. 4,436,684 to White ("White") relates to a method of forming implantable prosthesis for reconstructive surgery. A selected internal skeletal structure is measured by subjecting the body to radiant energy to produce radiant energy responses that are detected to obtain representations delineating the skeletal structure. Three dimensional coordinate data defining the skeletal structure is generated from the obtained representations. The coordinate data is employed to control a sculpting tool to form the prosthesis.
While the White patent discusses the use of radiant energy to obtain skeletal structure information utilized to fabricate a prosthesis, there is no teaching to use mathematically described anatomic joint surfaces, or archetypes, derived from the examination of other joints to create the prosthesis.